1. Field of the Invention
The invention relates to a back light source module, and more particularly, to a back light source module of liquid crystal device (LCD); the back light source module makes use of the arranging mode of a plurality of light sources to reduce the thickness of the back light source module, and moreover, to achieve a relatively better light mixing effect.
2. Description of the Prior Art
Most of the back light source modules of liquid crystal device of the prior art utilizes cold cathode fluorescent lamp (CCFL) as their light sources. Take direct-light-type back light source module for example, following trend of increasing the size of the liquid crystal device, in order to meet the requirement of certain specific luminance, the number of CCFL will increase accordingly. However, since the CCFL contains poisonous mercury, the quantity of utilization in the future will reduce following the ever-rising environmental consciousness.
Therefore, the manufacturers of the liquid crystal device are trying every possible ways to develop various types of substitute of light source in order to overcome the above-mentioned problems. Among them, Light Emitting Diode (LED) is a well-known one. FIG. 1 is a schematic diagram of a direct-light-type back light source module 101 of the prior art. As shown in FIG. 1, the direct-light-type back light source module 101 includes respectively a plurality of first light sources 11, a plurality of second light sources 12, and a plurality of third light sources 13, displaced in rows and columns on a backplate 30. There is a reflecting member 15 displaced among the first light source 11, the second light source 12, the third light source 13, and the backplate 30. In addition, the direct-light-type back light source module 101 has a thickness τ. One of the preferred light sources of the first light source 11, second light source 12, and the third light source 13 can be the above-mentioned LED.
This kind of LED can directly utilize a white light emitting diode (W-LED), or employ a three-original-color including red, green, and blue of light emitting diode (R-LED ; G-LED; B-LED) to perform light mixing.
TABLE 1 is a table of the comparison of the characteristics of various kinds of light source of the invention. As shown in TABLE 1, one can understand that the luminous uniformity and the chromatic intensity of the liquid crystal device employing CCFLs as light sources are relatively worse.
The comparison of the characteristics of various kinds of light source of the invention
TABLE 1Three-Three-original-colororiginal-CCFL(direct-color (side-(direct-light-type)light-type)light-type)Luminous uniformityXX◯Chromatic intensityX◯◯Module thickness◯X◯Light source◯X◯
Although performing light mixing by employing a three-original-color light emitting diode can obtain better chromatic intensity, it will result in the fact that the luminous uniformity is not good enough in the situation of employing direct-light-type back light source module since the LED is a light source having high orientation. In order to improve the luminous uniformity, i.e. to achieve an optimum light mixing effect, the thickness τ of the back light source module should be greater than the thickness of LCD employing CCFL as light source. Therefore, as far as the design of direct-light-type of back light source module is concerned, the light source employing three-original-color light emitting diode is not an ideal light source.
For comparison, the side-light-type back light source module that employs the mixing light of the three-original-color LED as light source has better luminous uniformity, chromatic intensity, and thinner module thickness, i.e. is a better light source. However, as comparing with the back light source module employing only the W-LED as light source, in order to achieve similar light mixing effect, its thickness τ is thicker than that of the back light source module that employs only the W-LED as light source. Moreover, as far as the power utilization and transfer are concerned, the white light emanated by the W-LED is not as strong as the white light mixed by the three-original-color light emitting diode.
FIG. 2 is the optical frequency spectrum of various types of light source. As shown in FIG. 2, the distribution of the optical frequency spectrum is in a range between 600 to 680 nm for the R-LED, in a range between 480 to 580 nm for the G-LED, and in a range between 450 to 530 nm for the B-LED respectively. As for the distributions of the optical frequency spectrum for CCFL light emitting diode, it is in a range between 400 to 700 nm. Therefore, the distribution of the optical frequency spectrum of the three-original-color light emitting diode, i.e. the R, G, and B LED, is narrower than that of the CCFL. As far as the normalized chromatic intensity is concerned, all the three-original-color LED including the R, G, and B ones can attain a value of 1 while the CCFL can attain a value of 1 only in a range between 530 to 550 nm. The value of the normalized chromatic intensity of the CCFL can only attain a value of less than 0.5 for the rest of ranges in the optical frequency spectrum except the above-mentioned range between 530 to 550 nm. Consequently, the chromatic intensity is relatively higher for the white light mixed by the three-original-color LED. Therefore, theoretically, the light source mixed by the three-original-color LED is still a good choice.